JP2002524231A - Preparation of catalysts for the synthesis of maleic anhydride by gas-phase oxidation. - Google Patents

Abstract

A method is provided for producing catalysts useful for synthesizing maleic anhydride by oxidizing saturated and/or unsaturated C4 hydrocarbons. A vanadium (V) compound is reacted with a mixture of phosphorous and phosphoric acids in a particular ratio, in a solvent mixture containing a structure former, and an entrainer and where the water of reaction together with entrainer is distilled off and the resulting precursor is subjected to calcination.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for converting saturated and / or unsaturated C ₄ -hydrocarbons into maleic anhydride (MS
A) A method for producing a catalyst for partial gas phase oxidation to

The production of maleic anhydride from C ₄ -hydrocarbons has been known for more than 20 years. In this case, a catalyst based on vanadyl phosphate (vanadyl pyrophosphate, vanadium-phosphorus-oxide) is used. The production of the vanadyl phosphate takes place via a catalyst precursor (precursor) which can be produced in an aqueous or organic medium. The precursor is then converted to the original catalytically active material in a second stage, before or after molding, in a reactor (in situ) or externally.

The reaction of C ₄ -hydrocarbons with a catalyst is carried out in different types of reactors. Fixed-bed reactors, fluidized-bed reactors and, therefore, riser reactors are used, in which fixed-bed reactors exclusively use vanadyl phosphate-based catalysts in the form of complete catalysts. EP 72381 and International Publication No. WO-A96 / 2
From US Pat. No. 5,230, the use of shell catalysts is also known.

[0004] The production of precursors is possible both in aqueous media and in organic media. In industrial technology, the method in an organic solvent is preferably used. In this case, isobutanol (2-methyl-propan-1-ol) is effective as a solvent or reaction medium. Catalysts made in aqueous media have distinctly less activity and selectivity, unlike catalysts made in organic media. This difference is due to the low specific surface area of the catalyst produced by the aqueous method. Furthermore, the use of organic solvents has the processing technical advantage inevitably in the form of easier separation of the formed precursor from the reaction mixture, since the product is insoluble in the solvent. Solvents must meet a series of prerequisites. That is, it must not react with, for example, the phosphorus compounds required for the formation of vanadyl phosphate. Furthermore, the boiling point is
It must vary within the range where the formation of the desired vanadyl phosphate is observed. As is generally known, reaction temperature significantly affects the rate of catalyst formation. Since the reaction is usually carried out in a boiling solvent, the boiling point of the solvent also plays an important role. In addition, solvents have a significant effect on the morphology of the reaction products and, in part, rather on the phases formed (Doi, T. Miyake, T .: Applied Catal. General 164 (1997), 141-148)
.

As a vanadium-containing starting material, vanadium pentoxide is generally used. Phosphoric acid is generally used as the phosphorus compound. Since vanadium is present in the target compound of oxidation stage IV, reduction with a suitable reducing agent is required. For this purpose, a number of compounds have been described. That is, for example, gaseous HCl, oxalic acid, benzyl alcohol, isobutanol, hydrazine or many other reducing agents are used. In this case, the nature of the reducing agent plays a secondary role in the reaction.

[0006] US Pat. No. 4,132,670 describes a process for preparing vanadyl phosphate catalysts. In this case, vanadium pentoxide is converted to the vanadin- (IV) compound in an alcohol, preferably isobutanol. In this case, the reduction of vanadium (V) to vanadium (IV) takes place depending on the solvent used. Subsequently, the precursor is produced using concentrated vanadium phosphate H ₃ PO ₄ . In this case, the water content of the reaction mixture in producing the precursor is described as an important parameter. In this case, a low reaction mixture water content is recommended.

From the description of US Pat. No. 4,382,876, the vanadium- (V) -compound is charged in isobutanol as solvent and H ₃ PO ₄ is added in small amounts as reducing agent. A method for producing a catalyst is known. In this case, the reduction of the vanadium- (V) -compound to vanadium- (IV) results according to the invention from a combined reducing agent consisting of a tertiary alcohol and phosphorous acid. The water formed in this way is distilled off discontinuously several times with the solvent. This process has the disadvantage that large amounts of water are repeatedly formed in the reaction batch, and this water is only distilled off after a certain time. Therefore, a low water content cannot always be maintained, which leads to poor performance of the later catalyst.

From the description of WO-A95 / 29006, a process for preparing vanadyl phosphate catalysts is likewise known. Also in this case, the vanadium- (V) -compound and phosphoric acid are reacted in isobutanol. In order to control the water content, the reaction water formed is prevented in this process by adding highly concentrated phosphoric acid to the reaction mixture. In this case, the total water content of the reaction mixture depends on the phosphorus compounds used (H ₃ PO ₄ 85%, H ₃ PO ₄ 100%, H ₃ PO ₄ or polyphosphoric acid 106
%) And the water formed during the reaction (by reduction of the vanadium (V) compound to the vanadium (IV) compound). The major disadvantages of this method are the high cost and the difficulty in handling with concentrated phosphoric and polyphosphoric acids.

The conversion of the starting material to the desired vanadyl phosphate can be carried out in basically different ways: Reduction of vanadium (V) -compound to vanadium (IV), vanadyl (IV
1.) subsequent reaction with a phosphorus compound to make phosphate; Reaction of a vanadium (V) -compound with a phosphorus compound to give the corresponding vanadium (V) phosphate, followed by reduction to vanadyl (IV) phosphate,
Or 3. Parallel reduction and conversion to vanadyl (IV) phosphate by reaction with phosphorus compounds.

After the end of the reaction, the vanadyl phosphate present in the suspension or in the solution is separated from the reaction mixture by a suitable method, for example by filtration or evaporation, dried and dried in another step, the so-called calcination. Alternatively, the catalyst is activated in the activation. Shaping for use in a fixed-bed reactor is performed before or after calcination, for example by tableting or extrusion. Another method of shaping lies in the production of shell catalysts, for example shell catalysts are also used in other processes, for example in the synthesis of phthalic anhydride from o-xylol or naphthalene.

[0011] The calcination of the precursor, ie the conversion to the original catalyst, is accomplished by converting C _4- to maleic anhydride.
It can be carried out externally where the conversion of the hydrocarbons is carried out as well as in the reactor (on site).

From the description of US Pat. No. 4,382,876, a process is known in which the precursor obtained in the first step is converted in the second step into the actual catalyst in the reactor itself. . In this case, the precursor is heated with a gradient of less than 1 ° C. per minute for activation, avoiding hot spots in the catalyst. At that time, calcination in the field C ₄ -
It is carried out in the presence of hydrocarbons and air, in which case it is heated to a temperature between 450 ° C and 510 ° C. After this temperature is maintained for about 12 to 72 hours, it is slowly cooled again.

A major disadvantage of this process is that the final working capacity of the catalyst is only achieved after a few hundred hours.

[0014] Along with the calcination process described above, external formation is also known. International Publication Number WO-A
No. 95/29006 describes a calcination method by converting a precursor in an atmosphere consisting of air, water vapor and an inert gas. In this case, the precursor is slowly heated in several steps at a heating rate of less than 1 ° C. per minute to a temperature of 350 ° C. to 550 ° C. This temperature is maintained for 2-8 hours, in which case an average oxidation step of vanadium of less than +4.5 occurs. A similar method of external calcination is known from the description of US Pat. No. 5,185,455 A. In this case, the tableted precursor is heated stepwise under a defined gas atmosphere to a temperature of 425 ° C. (gradient 250 ° C.).
Until the first temperature) and at this temperature for 6 hours. In this case, the oxygen content and the water content of the calcining gas play an important role in relation to the subsequent working capacity.

These methods, on the other hand, are economical because they do not shut down the reactor with small yields over several weeks until the catalyst is completely formed, as in the case of in-situ calcination. There are advantages. On the other hand, during external calcination, precursors can be formed in smaller fractions, which allows for continuous quality control, thereby putting the entire catalyst charge at risk of loss. There is no. By external calcination, the conditions (eg oxygen content and temperature) required for optimal formation of the precursor for the active catalyst can be assured more uniformly and better. In contrast, in-situ calcination in a fixed-bed reactor results in a non-uniform conversion of the catalyst over the length of the reactor or reactor tubes.

In general, during external calcination, the precursors are usually in a defined gas atmosphere (
(A gas mixture consisting of oxygen, inert gas and water vapor) and a precisely fixed temperature program. Catalysts formed in this way immediately show full working capacity, unlike catalysts calcined in situ. The oxygen content (control of the average oxidation stage of vanadium), the water concentration in the furnace atmosphere and the parameters of the temperature program (steepness of the temperature gradient, final temperature and residence time) influence the working capacity of the obtained catalyst. Is an important measure of impact.

[0017] In order to control the catalytic properties of the catalyst, US Pat. No. 4,132,670 A, EP 0 458 541 A1 and German Offenlegungsschrift 3
018849 (U.S. Pat. No. 4,251,390 A), International Publication No. WO-
A93 / 01155, U.S. Pat. No. 528,880 A recommends the addition of a large number of compounds as accelerators or doping substances at significantly different concentrations. In this case, for example, the elements Mo, Zn, Fe, Co, Li, Ce, Zr
, U, Bi and Cr are used, in which case the atomic ratio of vanadium: promoter element is described in the range from 1: 0.2 to 0.001. in this case,
The addition of the accelerator may take place at various points in the manufacturing process. Techniques in which the addition takes place during the conversion to the precursor (uniform distribution of the accelerator in the precursor), and thus an impregnation method in which the pre-synthesized precursor is superficially applied with the accelerator. Is used.

[0018] To control the structure of the catalyst formed, European Patent Application Publication No. in 0,151,912 Pat, alcohol-modified soluble surface active substances such as HI, the use of SO ₂ or oleum is described.

With the use of promoters, the incorporation of inert materials to control catalytic activity has also been described. As the inert additive, for example, SiO ₂ , TiO ₂ and silicon carbide are described. The addition of these substances generally takes place after the end of the synthesis of the precursors and before the formation of the catalyst.

[0020] Furthermore, recently, the use of additives for controlling the pore structure of the molded catalyst used has been described. In this case, for example, a certain amount of high alkanoic acid is added to the dried precursor before molding. In an additional process step, these substances, after formation, can eventually be removed again from the shaped body, thereby achieving the defined pore structure.

The described processes for preparing catalysts for the synthesis of maleic anhydride all have a series of disadvantages. That is, corrosion is increasing in the apparatus due to reduction of vanadium V using, for example, hydrogen chloride gas. The resulting chlorine offgas and chloride waste must be disposed of at high cost and partially contaminate the precursor. Another disadvantage is associated with the large amount of water that results from the reaction. The processes described in the prior art for removing water from the reaction mixture degrade the performance of the subsequent catalysts or can be carried out at high cost and expense, for example only with polyphosphoric acid.

[0022] Therefore, the task was presented of describing a method for preparing a catalyst for the synthesis of maleic anhydride by gas-phase oxidation, which eliminates the disadvantages mentioned above.

The object of the present invention is to react a vanadium (V) -compound with a mixture of phosphorous acid and phosphoric acid in a solvent mixture, so that a saturated and / or unsaturated vanadyl phosphate-based compound is obtained. Is a method for producing a catalyst for synthesizing maleic anhydride by oxidizing C ₄ -hydrocarbons, wherein the ratio of H ₃ PO ₃ / H ₃ PO ₄ − is 1: 1 to 1: 2. And as a solvent a structure-forming agent from the group comprising isobutanol, mono- and polyfunctional alcohols, amines, organic phosphates, organic phosphites and organic phosphonates, alkyl aromatic compounds and A mixture of entrainers from the group comprising cycloalkanes is used, the molar ratio of vanadium to structure former being in the range from 10: 1 to 100: 1. There, characterized by the water of reaction with entraining agent continuously distilled off at boiling temperature, subsequently to calcining precursor thus obtained.

The vanadium- (V) -compounds are agents which influence the structure of vanadyl phosphate, such as benzyl alcohol, isobutanol, and auxiliaries which allow the removal of formed and / or added water (for example “entrainment” Agent)). The suspension is heated and, after reaching the boiling point, a mixture of phosphorous acid and phosphoric acid is added. As the vanadium- (V) -compound, vanadium pentoxide is preferably used. It is also possible to use other vanadium- (V) -compounds, for example their oxychlorides.

As the phosphorus component, phosphorous acid and phosphoric acid are used. Phosphorous acid is used as a reducing agent for vanadium (V) as well as a phosphorus source. In this case, the use of another reducing agent is dispensed with. Phosphorous acid is preferably used in solid form to produce a mixture, but may also be used as a solution. Phosphoric acid having preferably 85 to 100% by weight, particularly preferably 85% by weight.
The phosphoric acid mixture is made by dissolving phosphorous acid in phosphoric acid, optionally with gentle heating. The mixture consisting of H ₃ PO ₃ / H ₃ PO ₄ comprises:
It has a molar mixing ratio of 1-1: 2.5, preferably 1: 1.5-1: 2.0.

The vanadium: phosphorus atom ratio of the amounts of vanadium and phosphorus used is 1: 0.9.
１ ： 1: 2.0. The vanadium-phosphorus compound thus obtained is
It has an average vanadium oxidation step of 3.85 to 4.3, in which case the vanadium-phosphorus-molar ratio in the isolated compound is in the range from 1: 0.9 to 1: 1.1. .

The addition of the mixture consisting of phosphorous acid and phosphoric acid takes place shortly after the boiling point of the vanadium pentoxide / solvent suspension has been reached. "Pre-reduction time" as described in other patent specifications is not used.

After the addition of the phosphorus component, the reaction batch is allowed to react for 4 to 24 hours, preferably 12 to 20 hours.
It is kept under reflux conditions for a period of time.

As a solvent in which the reaction is carried out, isobutanol (2-methyl-propane-1)
-All) is used. However, other inert solvents having a boiling point of about 100 ° C.,
For example, toluene can be used. The decisive point of the claimed method is that the addition of structurally modified drugs is required exclusively in small amounts.

As structural modifiers, the following classes of compounds can be used: monofunctional and polyfunctional alcohols, such as ethanediol, propane-1,3-diol, n-hexanol, diphenylmethanol, preferably Is benzyl alcohol and α-ω-alkanediol, monofunctional and polyfunctional amines,
For example n-propylamine, isobutylamine, ethylenediamine, preferably n-decylamine and propylenediamine, organic phosphates such as butylphosphate, dibutylphosphate, trimethylphosphate, preferably tributylphosphate, phosphite or phosphonate, such as methylphosphonic acid ,
Trimethyl phosphite, dibutylphosphonic acid, preferably tributyl phosphite, and thus mixtures thereof. Based on their chemical structure, these compounds may be incorporated (intercalated) into the precursor layer structure, i.e. they can influence the form of the material, i.e. the type and number of that formed. Regarding the number of moles,
The ratio of the structure modifier to the vanadium used is between 0.1% and 10%. The small amount required is that the process described herein can be carried out in such a way that the additive, in particular the benzyl alcohol additive, has a vanadium: additive molar ratio of 1: 0.5 to 1: 1.0. It is clearly distinguished from other manufacturing methods. Here, these added substances are used as reducing agents, in which case the effect of structural modification is not described when only small amounts are used (EP-A-0151912).

Furthermore, so-called “entrainers” are added to the reaction mixture, which allow the water introduced during the reaction to be removed from the reaction mixture. In this case, a series of substances can be used as entrainers. Generally, in addition, non-polar compounds are used which are only slightly miscible with water, such as alkylaromatics and cycloalkanes. Preferably, based on simple usability, toluene, xylol, cyclohexane and benzol are used. Particularly preferred is cyclohexane as an entraining agent. The amount added to the isobutanol varies within the range of 5 to 15% by volume, preferably 8 to 12% by volume of the amount of solvent used.

During the boiling of the reaction mixture, a ternary mixture consisting of the solvent, the entrainer and the resulting water of reaction is continuously withdrawn from the reactor via an external circulation. In this circulation, the ternary azeotrope is led into a vessel which allows the separation of the two-phase condensate and thereby the separation of the water-rich phase. The depleted mixture of water, consisting of the solvent and the entrainer, is fed back into the reactor. After separation, the amount of residual water in the returned mixture is 0.5% by volume.
Is less than. This method ensures that the water content of the reaction mixture can always be kept below 0.5% by volume. This is a decisive criterion for the selectivity and conversion of the resulting catalyst.

In the preparation of the precursors according to the invention, catalyst doping can optionally be carried out. Doping of the catalyst can be performed in various ways. On the one hand, the elements Mo, Wo, Bi, Cr, Co, Ni, Fe, Li
, Ce, Zr, U and Zn, preferably Mo, Cr, Bi, Co, Zn, Li
A metal compound in the form of a soluble compound of Ce and Ce with vanadium: doping element 1
: Can be added at an atomic ratio of 0.1 to 0.001. Another method is
After the completion of the reaction, immediately before drying or separation, the formed pre-catalyst substance is to be doped. Again, soluble compounds must be used to achieve a uniform distribution of the doping material. Examples of soluble compounds include chlorides of the above metals,
Carbonate, acetylacetonate, acetate and nitrate.

After the elapse of the reflux time, the separation of the precursor takes place. This can be done by filtration and subsequent drying. In this case, it is particularly advantageous to do this by spray-drying the suspension obtained.

After drying of the precursor, it can be converted to a shell catalyst, a catalyst for a process in a fluidized catalyst deposit, or a post-processing to a full contact catalyst for a fixed bed reactor,
Can be used directly. However, this requires that the precursors be in a form which is advantageous for the respective field of use. This formation can be, for example, tableting,
It can be done by agglomeration, extrusion or similar processes. The nature of the molding process and the resulting catalyst form and condition do not affect the applicability of the process. For molding, auxiliaries which influence the moldability and flowability of the crude material, for example, may be added. As auxiliaries, use is made, for example, of graphite, high alkanoic acids (eg stearic acid), polyethylene glycol and silicic acid, or mixtures thereof. Examples of the shape of the catalyst body include a cylinder, a sphere, and a ring.

Subsequently, the precursor is subjected to a calcination process, irrespective of the form obtained,
The precursor is brought into its original catalytically active form. In this case, the calcination can be performed in the reactor (on site) as well as in an external step. In this case, external calcination is advantageous because it results in a catalyst which is completely usable immediately after the process. In this case, the long formation steps which are observed in the case of in-situ calcined catalysts are dispensed with.

The calcination carried out within the scope of the process described here is carried out using the precursor dried as a powder or a compact, preferably in the following manner: Gas metering The precursor is charged in a suitable furnace system equipped with units for temperature control over time, for example in a fluidized bed furnace for powders or a kiln or tube furnace for shaped bodies. In this case, the parameters listed below relate to the external calcination of the whole catalyst: Calcination step: passivation In the first step, the passivation of the furnace chamber takes place at a temperature in the range from 20 to 100 ° C. using an inert gas. Nitrogen is preferably used as the inert gas. The time required for deactivation and the amount of inert gas should be calculated so that a residual oxygen content of less than 5% by volume in the furnace system is guaranteed.

[0038] 2. Calcination Step: Gradient 1 In the next step, the furnace system is fed with a gas mixture having an oxygen content of 5% to 20% by volume. The furnace temperature is then heated at a rate of 5C / min to 20C / min (gradient 1) to a temperature of 150C to 250C (final temperature 1). In some cases, this temperature can be kept constant for up to 3 hours.

[0039] 3. Calcination step: Gradient 2 After reaching final temperature 1 and elapse of the residence time, the heating of the system
Continue until a final temperature of 2 ° C. to 300 ° C. is reached. In this case, the heating rate is 1 ° C /
Min to 10 ° C./min and the gas mixture supplied to the furnace system is formed from components of oxygen, water vapor and an inert gas, wherein an oxygen content of 5% by volume and a water content of 50% by volume are obtained. Achieved. After the final temperature has been reached, in this case also 3
The residence time up to the time can be interposed.

[0040] 4. Calcination step: Gradient 3 After the end temperature 2 has been reached and the dwell time has elapsed, the system is heated to Gradient 3 at 380
Continue until a final temperature of 3 ° C. to 460 ° C. is reached. In this case, a gas mixture corresponding to the composition from gradient 2 is used. In this case, the heating rate is 0.1 ° C./min.
° C / min. This final temperature is maintained for between 2 and 8 hours while maintaining the gas composition.

[0041] 5. Calcination step: cooling phase After the end of the fourth calcination step, the furnace system is cooled to ambient temperature under inert gas.
After dropping below the temperature of 100 ° C., the furnace system can be opened and the catalyst removed. The catalyst is filled in a closed container.

The addition of steam during calcination is important because it positively affects the conversion of the precursor to catalytically active vanadyl pyrophosphate. Specimens treated without steam have clearly less catalytic activity. Air is preferred as the oxygen-containing gas. The oxygen concentration required for the individual calcination steps can preferably be obtained with a mixture of air and an inert gas, preferably nitrogen. In this case, the gas mixture consisting of air, inert gas and water vapor is 0.1-0.5: 0.1-
It can be used in a volume-mixing ratio of 0.5: 0.0 to 0.8.

As compared to the prior art, the calcination method used here is distinctly different in relation to the temperature gradient used. 150-250 to shorten the calcination process in time
Heating of the furnace system until a temperature of ° C. is carried out with a temperature gradient which is clearly increased with respect to the comparative description. In the present invention, a temperature gradient of 1 to 10 ° C./min is used. With a heating rate of up to 10 times compared to this state of the art, time is saved in comparison with comparable methods and thereby a more economically operated calcination method is provided. Moreover, the differences associated with the gas composition are in the individual calcination phases.

The preparation of the MSA catalyst is now described in detail by way of example: Example 1: Preparation of the MSA catalyst according to the invention In a mixture consisting of 2500 ml of isobutanol, 250 ml of cyclohexane and 16.2 g of benzyl alcohol (as structural modifier). To this was added 272.8 g of vanadium pentoxide under stirring in a 4 liter flask equipped with a stirrer, thermometer, dropping funnel and water drop separator. After heating the batch to boiling temperature, 85% phosphoric acid 2
A solution of 90.4 g of phosphorous acid in 25.7 g was added via dropping funnel in 2 hours. Simultaneously with the addition of the phosphoric acid mixture, the water which had been entrained with the acid mixture, or formed by the reaction, was removed via a water drop separator. Reflux conditions were maintained for 16 hours upon simultaneous drainage of water from the circulation. During this time, the color of the reaction mixture slowly changes from orange to green and changes to luminescent blue. Over the reflux time, 97 g of aqueous phase was separated by a water drop separator. After 16 hours, the water drop separator was replaced by cooling and a total of about 1700 ml of solvent were distilled off. The product (precursor) thus obtained was dried at 100-150 ° C. in a vacuum drying box.
About 550 g of precursor were obtained.

The precursor material was post-processed to a compact. In addition, 10 g of graphite was added to 250 g of the dried precursor powder and mixed vigorously. The added graphite must be evenly distributed in the material. After thorough mixing, using a tableting machine (type: Fette Exakta E1),
A cylindrical press having a diameter of 5 mm and a height of 5 mm was produced. The mass of the pressed product was about 120 mg.

The calcination of the shaped bodies was carried out according to the temperature program and the gas volume program described in Table 1:

[0047]

[Table 1]

MSA—Measurement of the catalytic properties of the catalyst: An 11 cm long deposit of the catalyst to be tested was produced in a quartz tube (internal diameter: 19 mm) in an electrically heated tubular furnace (deposit volume: 31.2 ml). The measured amount of catalyst was recorded. A thermocouple (Ni / CrNi) was additionally arranged in the sediment to enable the measurement of the reaction temperature. A rotameter or mass flow controller (Fa. Brooks, type: 585) for metering gas to air and butane
80E) was used. The test, 0.83% by volume of butane concentration and 1165H ^- corresponding to ¹ gas velocity, 600Mln / min air amount and n- butane 5ml
n / min was used. The maleic anhydride formed is collected in a wash bottle filled with water over a known time and titrated against 0.1 n NaOH using phenolphthalein as indicator by triclinic system Was measured. By switching off the corresponding valves, the starting mixture as well as the exhaust gas are analyzed after removal of the condensable content using a flame ionization detector (= FID, modified gas chromatograph Hewlett-Packard HP5890II),
And thereby the conversion could be measured. M formed per hour
From the amount of SA and the amount of butane used during this time, the yield, conversion and selectivity were calculated.

The conversion, yield and selectivity are evident from the following relation: Conversion:

[0050]

(Equation 1)

Yield:

[0052]

(Equation 2)

Selectivity: S [%] = A / U The change in volume during the reaction is a variation within a few percent, and by-products are formed in only small amounts with CO and CO _2. Therefore, the yield calculation could be performed by the above chemical equation.

Description of symbols used: U: conversion A: yield S: selectivity Int (in / out, X): FID-signal intensity at entrance or exit n (in / out): entrance or exit V (in, C ₄ ): n-butane gas flow, mol / h = c (in, C ₄ ) ★ v (i)
n, total), c (in, C ₄ ) = 0.83% by volume, v (in, total) = 27 mmol / h = 6
05 mln / ht: reaction time, h The by-products optionally formed and the by-product concentrates could be determined by analyzing the wash water using ion chromatography. It was noted that the catalyst temperature did not exceed 480 ° C. during the test run. Otherwise, damage to the catalyst could be feared. To determine the catalyst, the furnace temperature was varied until maximum yield was achieved. The temperature and conversion at the maximum yield were referenced for catalyst determination.

Example 2 (Comparative): Preparation of MSA-catalyst according to International Publication No. WO-A95 / 29006 In a 10 liter 4-neck flask equipped with stirrer, thermometer, reflux condenser and heater, 6480 ml of butanol (= 5196 g), benzyl alcohol 7
A mixture consisting of 20 ml (750 g) was charged. 670 g of vanadium pentoxide were added to the mixture with stirring. The reaction mixture was then heated to reflux and maintained under these conditions for 3 hours. Subsequently, the mixture is cooled to about 20 ° C. below the boiling temperature,
Then 816 g of 106% of freshly produced phosphoric acid were added. The mixture thus obtained was then heated to fresh reflux and maintained under these conditions for 16 hours. After 16 hours, the reaction mixture was cooled to about 50 ° C. and filtered. A luminescent blue filter cake was obtained, which was wrapped in a shell and dried in an air-circulating oven at 150 ° C. for 10 hours. About 1300 g of a grey-blue catalyst precursor powder were obtained.

The dried powder is passed under a light pressure through a 65-mesh sieve, about 4% by weight of graphite is added, and a 4 * 4 mm-sized cylindrical tablet is put into a tableting machine (type: Fette Exacta). Fette Exakta) E1). The pressed product thus obtained was calcined under the following conditions.

[0057] 100 ml of the precursor tablets were placed in a tube furnace in a glass tube having a diameter of 5 cm. Prior to the start of the temperature program, a gas mixture having an oxygen content of 5% by volume as air / nitrogen mixture (160 l / h) was passed into the furnace. The furnace system was then heated using a heating rate of 0.5 ° C / min to a temperature of 150 ° C. Fifteen
After reaching 0 ° C., the composition of the gas mixture was changed, ie a gas mixture having a composition consisting of 25% by volume of air, 25% by volume of nitrogen and 50% by volume of steam was used. The temperature was then further raised to 420 ° C. and maintained for 4 hours. After cooling, the catalyst was tested for catalytic performance as described in Example 1.

Example 3, Comparative Example: EP-A-0036623 (US Pat.
Preparation of MSA-catalyst according to 382876) 103.3 g of phosphorous acid and 352.8 g of 85% phosphoric acid were dissolved in 2.8 liters of isobutanol. 327.4 g of vanadium pentoxide in the resulting solution
Was suspended and the reaction batch was heated to boiling temperature. Approximately 500 ml of the condensate was withdrawn from the reflux in 30 to 60 minutes. Subsequently, the batch was kept under reflux conditions for a further 5 hours. After cooling to ambient temperature, it is filtered and the pale blue reaction product is
Dry for 2 hours in vacuo (25-50 hPa). About 68 gray pre-catalyst powders
0 g was obtained. Next, 3% by mass of graphite was added to this powder and pressed into a pressed product having a diameter of 5 mm and a height of 5 mm.

The calcination of the precursor was carried out in this way in the field, ie in a pilot reactor, as follows: The reaction tube was filled with catalyst-precursor-tablet (fill height: 240
cm, internal diameter: 25 mm). Subsequently, 500 L / h of air was passed through the catalyst,
The reactor was heated to 200C. The reactor temperature was increased from 200 ° C. to 330 ° C. in 26 hours while passing more air. When reaching 330 ° C., a gas mixture consisting of C ₄ -hydrocarbons having a concentration of 1.45% by volume (about 70% by volume of butene,
n-butane (30% by volume) at a gas velocity of 1700 h-1. Next, the furnace temperature was increased until a hot spot temperature of 500 ° C. was obtained. Then, C 4 _- air mixture, the same concentration of butane - air - was replaced by the mixture.
Upon conversion to the butane-air-mixture, the hot spot temperature settled, requiring a new adjustment of the furnace temperature until a hot spot temperature of 500 ° C. was again obtained. The temperature was maintained over a period of 24 hours, and butane - was increased to ^{1 -} under maintenance of the air mixture gas velocity 1700h ^- from ¹ 2300H. 8 to 1
In 4 days, further activation of the catalyst took place, in which case care had to be taken that the conversion of butane did not exceed 90%. The conversion was adjusted by adjusting the furnace temperature.

A comparative test was carried out in a laboratory reactor according to Example 1 using the catalyst formed by the method described above.

Example 4 Preparation of an MSA-Catalyst According to the Invention Using an Amine as a Structural Modifier The preparation of the catalyst was carried out according to the method described in Example 1. However, instead of benzyl alcohol, 1-aminododecane (vanadium: aminodecane 1: 0.0
5) 27.8 g were added to a mixture consisting of isobutanol and cyclohexane. Processing was performed as described in Example 1.

Example 5 Preparation of an MSA-Catalyst According to the Invention Using a Phosphorus Compound as a Structural Modifier The preparation of the catalyst was carried out by the method described in Example 1. The addition of the structure modifier is preferably effected in this case by means of a phosphoric acid mixture. To this mixture was added 37.5 g of tributyl phosphite (vanadium: tributyl phosphite = 1: 0.05) and to the reaction mixture as described in Example 1. Processing was performed as described in Example 1.

Example 6 Preparation of an MSA-Catalyst According to the Invention with the Addition of a Promoter a) The preparation of the catalyst was carried out by the method described in Example 1. In this case, a cobalt compound soluble in the solvent mixture used (for example cobalt acetylacetonate = Co (acac) 2) was used as promoter. In the solvent obtained from Example 1,
Co (acac) 2 (aca) corresponding to a vanadium: Co- ratio of 1: 0.02.
15.43 g of c = pentane-2,4-dione, acetylacetone) were added.
The remaining reactions and processing were performed as described in Example 1.

B) In this example, the impregnation of the formed precatalyst with a doping substance is described. After the preparation of the precatalyst material according to Example 1, the reaction mixture before the solvent separation, after drying 1:
Zn in 100 ml of isobutanol, corresponding to a vanadium: Zn ratio of 0.02 (
acac) 2 15.81 g of solution was added. After mixing, the reaction mixture was processed by a drying method. Further processing and calcination were performed as described in Example 1.

Comparative testing of MSA-catalysts according to methods 1 to 3: The catalysts to be tested were prepared according to the methods described in methods 1 to 3 (including formation or calcination). The test itself was performed in a laboratory reactor as described in Example 1. In this case, the temperature of the furnace system was varied until maximum yield was obtained. The test results (for maximum yield) are summarized in the following table:

[0066]

[Table 2]

From the above table, the superiority of the process described herein compared to Method 3 is clearly evident. In this case, the superiority over method 3 is indicated, on the one hand, by a 6.5 mol% higher yield at a furnace temperature of 10 ° C. lower. At the same time, about 8 for maximum yield
The relatively low conversion of 8% also indicates the low activity of the catalyst prepared by Method 3.

The advantage of the production method 1 according to the present invention over the method 2 is not particularly significant. However, a higher yield of 1.4 mol% of the catalyst prepared by the process according to the invention was found. The significance of this difference in yield becomes apparent when the total overproduction by such catalysts is compared using the cost of catalyst loading. The difference in yield on said scale results in the expense for catalyst loading within the catalyst life being made economic with higher yields.

In summary, the test results show a clear advantage of the manufacturing methods described herein. In addition, the elimination of highly concentrated polyphosphonic acid (according to method 2) and the use of phosphorous acid as reducing agent result in obvious handling advantages. Through the use of doping elements or structural modifiers ('templates'), the activity of the catalyst can be maximally tailored.

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] November 16, 2000 (2000.11.16)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

The object of the present invention is to react a vanadium (V) -compound with a mixture of phosphorous acid and phosphoric acid in a solvent mixture, so that a saturated and / or unsaturated vanadyl phosphate-based compound is obtained. Is a method for producing a catalyst for synthesizing maleic anhydride by oxidizing C ₄ -hydrocarbons, wherein the molar ratio of H ₃ PO ₃ / H ₃ PO ₄ is from 1: 1 to 1: From the group comprising isobutanol, monofunctional and polyfunctional alcohols, monofunctional amines 0 and polyfunctional amines, organic phosphates, organic phosphites and organic phosphonates as solvents A mixture of entrainers from the group comprising the structure formers, alkylaromatics and cycloalkanes, wherein the moles of vanadium and structure former are used. Is within the range from 10: 1 to 100: 1, and the reaction water containing the entrainer is continuously removed from the circulation at the boiling point, in which case the residual water content of the circulating liquid of the reaction mixture and the residual water content resulting therefrom. The water content is less than 0.5% by volume and the precursor thus obtained is subsequently calcined, using a temperature program consisting of three gradients, in which case the gradients are: → Gradient 1: starting temperature 50 ° C or less, heating rate 5-20 ° C / min, final temperature 100-
250 ° C., residence time 0 to 3 hours, → Gradient 2: starting temperature Final temperature of gradient 1, heating rate 1 to 10 ° C./min, final temperature 1
50-300 ° C., residence time 0-3 hours, → Gradient 3: starting temperature Final temperature of gradient 2, heating rate 0.1-3 ° C./min, final temperature: 380-460 ° C., residence time 2-8 hours During the temperature gradient, a gas mixture consisting of air, inert gas and water vapor is
. It is characterized by using a volume mixing ratio of 1-0.5: 0.1-0.5: 0.0-0.8.

────────────────────────────────────────────────── ─── Continuation of front page (71) Applicant Zielstattstraβe 20, D-81379 Munchen, F.C. R. Germain (72) Inventor Joachim Lotz Germany Klingerstrasse 44, Germany (72) Inventor Hans-Jürgen Eberle Germany Munich Alfred-Kubin-Weck 44 F-term (reference) 4C037 KB02 KB04 KB12 4G069 AA02 AA08 BA08A BA08B BA21C BB14A BB14B BC04A BC25A BC35A BC43A BC47A BC51A BC54A BC54B BC58A BC59A BC60A BC66A BC67A BC68A BE05C BE14C BE25C BE36C BE37C CB14 DA05 EA02X EA02Y FA01 FB30 FC65 FC02 FC65 FC02 FC06 FC02 FC02

Claims (13)

[Claims] 1. The reaction of a vanadium (V) -compound with a mixture of phosphorous acid and phosphoric acid in a solvent mixture results in a saturated and / or unsaturated C _4- based on vanadyl phosphate. by oxidizing hydrocarbons, a process for the preparation of catalysts for the synthesis of maleic _{acid, H 3 PO 3 / H 3} P
The O ₄ -ratio is from 1: 1 to 1: 2.5, and the solvent is isobutanol, monofunctional and polyfunctional alcohols, monofunctional and polyfunctional amines,
A mixture of a structure-forming agent from the group comprising organophosphates, organic phosphites and organic phosphonates, an entrainer from the group comprising alkylaromatics and cycloalkanes is used, in this case with vanadium and Molar ratio with the agent is 10: 1 to 1
For the synthesis of maleic anhydride, characterized in that the reaction water containing the entrainer is continuously distilled off at the boiling point and the precursor thus obtained is subsequently calcined. Method for producing catalyst. 2. The vanadium: phosphorus atom ratio between the amounts of vanadium and phosphorus used is in the range from 1: 0.9 to 1: 2.0, and the compound thus obtained is 3.85. 2. An average vanadium oxidation step of .about.4.3, wherein the vanadium-phosphorus molar ratio in the isolated compound is in the range of 1: 0.9 to 1: 1.1. The described method. 3. Structural modifiers such as ethanediol, propane-1,3-diol, n-hexanol, diphenylmethanol, benzyl alcohol, α-
ω-alkanediol, n-propylamine, isobutylamine, ethylenediamine, n-decylamine, propylenediamine, butylphosphate, dibutylphosphate, trimethylphosphate, tributylphosphate, methylphosphonic acid, trimethyl phosphite, dibutylphosphonic acid and tributyl phosphite 3. The method according to claim 1 or 2, wherein one or more compounds from the group comprising are used. 4. The process as claimed in claim 1, wherein one or more compounds from the group comprising toluene, xylol, cyclohexane and benzol are added as entrainers. 5. The process as claimed in claim 1, wherein water is continuously removed from the circulation during the reaction and the residual water content of the circulating liquid is less than 0.5% by volume. 6. The reaction mixture contains the elements Mo, Wo, Bi, Cr, Co, Ni,
The one or more doping substances in the form of soluble compounds of Fe, Li, Ce, Zr, U and Zn are added in a vanadium: doping element atomic ratio of 1: 0.1 to 0.001. 6. The method according to any one of 1 to 5. 7. The compound obtained is, after drying, fed with one or more auxiliaries, preferably graphite, and shaped by tableting, agglomeration and extrusion into suitable shaped bodies. 7. The method according to any one of claims 1 to 6. 8. The process as claimed in claim 1, wherein the moldings obtained in this way are converted into the active compounds externally or in situ by a suitable calcination method under defined gas concentration and temperature conditions. Or the method of claim 1. 9. In the case of external calcination, a temperature program consisting of three gradients is used, in which the gradients are: → Gradient 1: starting temperature 50 ° C. or less, heating rate 5-20 ° C./min, final temperature 100. ~
250 ° C., residence time 0 to 3 hours, → Gradient 2: starting temperature Final temperature of gradient 1, heating rate 1 to 10 ° C./min, final temperature 1
50-300 ° C., residence time 0-3 hours, → Gradient 3: starting temperature Final temperature of gradient 2, heating rate 0.1-3 ° C./min, final temperature: 380-460 ° C., residence time 2-8 hours 9. A method according to any one of the preceding claims, wherein the method is formed as follows. 10. A volumetric mixture of air, inert gas and water vapor of 0.1 to 0.5: 0.1 to 0.5: 0.0 to 0.8 during the temperature gradient. 10. The method according to claim 1, wherein the method is used in a ratio. 11. The method according to claim 1, wherein the calcination system is inerted with an inert gas before the start of the temperature program, so that an oxygen content of less than 5% by volume is achieved.
The method according to any one of claims 1 to 10. 12. The method according to claim 1, wherein after the completion of the temperature program, the calcination system is cooled to a temperature below 100 ° C. under an inert gas atmosphere.
The method described in the section. 13. A catalyst for the gas-phase oxidation of C ₄ -hydrocarbons to maleic anhydride, obtainable by the process according to claim 1.